1. Field of the Invention
This invention concerns copper phthalocyanine-dyes and dye solutions especially valuable for dyeing paper. Use of these dyes provides blue paper whose color does not bleed in contact with common household substances such as milk, grease or household cleaners.
2. Prior Art
Copper phthalocyanine is widely known as useful for dyeing paper, at least when it is disubstituted with amino-methyl groups or when it is sulfonated. The outstanding light fastness and high tinctorial strength of copper phthalocyanine makes it unique among pigments, and from the time of its discovery dye manufacturers have directed their efforts to the discovery of a solubilized form suitable for textile dyeing and printing. Sulfonation gives a soluble product which has excellent strength and light fastness but is not fast to water-treatments, especially washing. Moreover, many dyes of this type, when used on dye-absorbent paper such as used for paper towels or handkerchiefs, tend to bleed when the paper is contacted with such materials as milk, grease or household cleaners. Since such paper must be very absorbent in order to be useful, very little or no alum and size can be applied. For instance, in the dyeing of so-called "tissue dyeings" no alum or size is used.
German patent application DT No. 2508892, Toji to Du Pont, published Sept. 4, 1975, discloses dyes of the formula CPC--(CH.sub.2 N.sup.+HR.sub. 1 R.sub.2 X.sup.-).sub.n where CPC is copper phthalocyanine n is 3 or 4, R.sub.1 is hydroxyalkyl or H but is at least 25% hydroxyalkyl, R.sub.2 is H, alkyl or hydroxyalkyl, and X is a solubilizing anion. These dyes have high water-solubility and also resist leaching from paper. The methods for synthesizing these dyes either employ bischloromethyl ether or produce some of this very objectionable carcinogen as a by-product. Extreme precautions must be taken to protect personnel when bischloromethyl ether can be present, thereby exacting an economic penalty.
While dyes in powder form have been used to dye paper for many years, there is now a wide use of dye solutions containing at least 15%, and preferably 20% or more of active dye. Such solutions are very desirable for paper dyeing where the correct duplication of shade can be a problem, and where the "dusting" of dry dyes can be another problem. Unfortunately, a dye having the high solubility desired for use in the dyeing of paper may also be susceptible to bleeding from the resultant colored paper, particularly when no alum or size has been applied.